Origins, tracks, and processes resulting in summertime atmospheric ridges in North America

This study investigates spatial and temporal characteristics (origins and tracks) of summertime upper level ridges (defined by daily zonal anomalies of geopotential height at 500 hPa) over North America. First we implement a ridge tracking scheme to locate where these upper level ridges originate, and then identify the multi-day paths of these objects. We then use backward air parcel trajectory analysis to identify the contribution of diabatic (‘moist’ processes from latent heating due to condensation) versus adiabatic (‘dry’ process from horizontal and vertical thermal advection) heated airstreams resulting in North American summertime ridges. Motivated by studies showing a significant contribution of diabatically warmed air in strengthening the record-breaking 2021 Pacific Northwest “heat dome”, we also investigate differences between surface temperature anomalies associated with ridges dominated by adiabatically versus diabatically heated air parcels over all of North America. Analysis presented here contributes to a growing body of research on the importance of upstream diabatic heating on the maintenance and intensity of atmospheric blocking by using a broader definition of an upper level high pressure system which captures a wider range of feature characteristics beyond the traditional “blocking” structure (including both open ridges and closed anticyclones). Additionally, most studies have focused on the characteristics of upper level high pressure features in Northern Hemisphere “blocking centers”, typically the North Pacific, North Atlantic, and over Russia. By analyzing North America, we aim to increase our understanding of ridges that occur in infrequent locations yet often have major impacts on society via driving surface extremes.